Meet the Winners:
2026 BioOne Ambassador
Invisible Enemies: The secret battles fought in blood
The first House Finch (Haemorhous mexicanus) I held in San Luis Potosi, Mexico amazed me. Small, light, and full of life, with that bright red head, bright like the tiny drop of blood I collected. I released him but his secret stayed hidden in my hands, silent inside that drop.
All of the finches we sampled looked active, energetic, even happy, but examining the tiny drops of blood told a different story. The birds were fighting invisible wars with Mycoplasma gallisepticum, a bacterium that originally affected only poultry but is now found in wild birds in the United States, and haemosporidia, blood parasites related to avian malaria. Either infection alone challenges a bird’s immune system. But when both attack together — a co-infection — the impact on the bird is amplified.
In a collaborative effort between Cornell University and multiple Mexican academic institutions, the research aimed to identify the presence of these microbes in wild House Finches in Mexico and understand their effect on the bird. We sampled wild finches across 12 states in Mexico, and what we found alarmed us: 74% were infected with the poultry bacterium, and 43% carried the malaria-related parasites. Many were battling both at once, and yet showed no signs of illness.
So, what were these microbes doing behind the scenes while the birds still looked healthy, their feathers smooth, their eyes clear and open, not swollen or crusted as in visibly sick birds?
To reveal this silent battle, we focused on the white blood cells, the immune defenders that behave like tiny soldiers attacking infections. Some of these soldiers, called heterophils, are the emergency first responders that rush to fight infection. Others, called lymphocytes, support long-term immunity and help keep the immune system balanced. When a bird is fighting an infection, its immune system is under stress, and its energy and resources are redirected toward immediate defense. As a result, the balance between these two types of cells changes: the emergency soldiers increase, while the long-term defenders decrease. This balance is called the heterophil-to-lymphocyte (H:L) ratio, and it is our measure of stress.
This ratio made the hidden damage to the finches visible. Birds infected with both microbes had much higher H:L ratios, indicating their immune systems were working overtime. Furthermore, the two infections acted like partners, each one making the other more damaging.
Critically this shows invisible infections can impact wildlife health long before any symptoms appear. This was also the first report of Mycoplasma gallisepticum infecting wild birds in Mexico; a bacterium once restricted to poultry, and already known to affect wild birds in the United States, had now spread into Mexican natural ecosystems, carried silently by birds as they moved across landscapes.
Why does that matter? Because stress weakens survival. By reducing a bird’s ability to feed, evade predators, and withstand harsh weather, stress not only threatens individual lives but also helps microbes spread to new species and new regions. Moreover, House Finches are not alone. Invisible infections are likely affecting many wildlife species, quietly reshaping ecosystems before we ever notice.
By revealing the presence of infection before symptoms appear, our research turns that tiny red drop of blood into an early warning, a red flag for wildlife health. It shows how multiple microbes interact, how stress influences behavior and survival, and how human-associated diseases can spread through ecological networks and even spill back into human environments.
This knowledge empowers conservation, urban planning, wildlife rehabilitation, and public health, because the boundaries between human and animal diseases are narrowing. We share more than a planet, we share diseases. When wildlife suffers silently, we will all eventually suffer the consequences.
I realized sometimes saving wildlife starts with a single drop of blood and something so small could carry the story of an entire species, indeed an entire universe. With every blood sample I examine, I witness a tale that the birds cannot tell in their songs, but I can make their hidden battles visible to the world. Protecting biodiversity is not only about preventing extinctions, but about safeguarding the delicate systems that sustain us all. By exposing invisible threats before they become visible crises, we give ourselves time to protect the fragile life around us.
Blood of a feather reminds us that protecting wildlife health is protecting our own world.
This summary is in reference to:
Journal of Wildlife Diseases, 61(2): 334-347 (2025)
María Teresa Reinoso-Pérez, Keila V. Dhondt, Andrés Alejandro Yánez Abad, Víctor Manuel Rodríguez-García, André A. Dhondt
Profile: Dr. Maria Teresa Reinoso-Perez
What drew you to the research topic you explored in your submission?
I was drawn to this research because of a question that emerged from my own observations. In the United States, house finches have been known to be affected by this bacterial disease for more than 30 years. However, during my Master’s research in Mexico, I never observed house finches showing those same symptoms. This contrast made me wonder whether the pathogen was already circulating in Mexico but had gone undetected. For my doctoral research, I set out to investigate that possibility, combining fieldwork and molecular tools to better understand how the disease spreads across regions. This question allowed me to connect my background in Mexico with research in the United States and explore disease dynamics at a continental scale.
How do you see your work contributing to public policy, citizen science, and/or science education more broadly?
My work contributes by improving how we detect and understand diseases affecting wildlife. This is especially important because the bacterium we study can be shared between wild birds and poultry, making it relevant not only for conservation but also for the poultry industry. By sharing findings in accessible ways and collaborating across regions, I aim to strengthen public understanding of the connections between environmental change, wildlife health, and human well-being through a One Health perspective.
What are your continuing research goals for the future (near or far)? What topics, areas, subjects are you interested in exploring?
My continuing research goals focus on understanding how environmental change influences the emergence and spread of infectious diseases in wildlife.
Lyndell Whyte
Communications officer, Wildlife Disease Association